1. Field of the Invention
The present invention relates generally to portable timepieces and, more specifically, to a portable watch in which a crown is held so as not be turned unintentionally or carelessly by utilizing engagement of screws.
2. Description of the Prior Art
Conventionally, a crown for operating a watch movement incorporated in a case band is a single component and includes a crown shaft section that moves the watch movement in association with the crown shaft section and a crown head that is formed integrally with the crown shaft section. The crown shaft section is inserted in a winding stem pipe, which is attached to the case band, and the crown head is fitted into a pipe end, which is located outside the case band, of the winding stem pipe.
There is known a portable watch in which, in order to prevent this crown from being turned carelessly, a male screw section is formed on an outer periphery of the pipe end, which is located outside the case band, of the winding stem pipe, and a female screw section is formed in the crown head to detachably engage the male screw section at the pipe end (see JP-A-57-46181 (page 1, right column, line 8 to page 2, left column, line 7, and FIGS. 1 and 2)).
In this portable watch, in a normal state in which the watch movement is not operated, the crown is engaged with the male screw section of the pipe to bring the crown head into abutment against an outside surface of the case band, whereby careless turn of the crown can be controlled. An operation for holding the crown so as not to be turned carelessly will be hereinafter referred to as a screw lock operation, and a state in which the crown is held will be hereinafter referred to as a screw lock state. In addition, when the watch movement is operated, the winding stem connected to the watch movement can be turned together with the crown after the engagement of the crown with the male screw section is released to bring the crown into a pulled state.
Incidentally, a mechanical portable watch, in which a watch movement operated by a winding stem has a spiral spring as a drive source, is made such that, in a state in which a crown is arranged in a position where the crown is not pulled out, the spiral spring is wound up by a turning operation for this crown. In addition, a portable watch, in which a watch movement operated by a winding stem has plural operation modes, is made such that, in a state in which a crown is arranged in a position where the crown is not pulled out, the operation modes are switched by a turning operation for this crown.
A state in which a crown is arranged in a position where the crown is not pulled out is generally referred to as a “zero stage”. On the other hand, a position where the crown is pulled out for calendar adjustment or the like is generally referred to as a “first stage”. There is also known a portable watch in which, depending upon a situation, a crown can be pulled out to a pulled-out position of a “second stage” that is a position for time setting.
It is undesirable to apply the technique of the JP-A-57-46181 to a portable watch, which has a function of winding up a spiral spring with a crown arranged in a “zero stage”, or a portable watch, which has a function of changing an operation mode, due to the following reasons.
That is, in the portable watch of the JP-A-57-46181, the crown shaft section and the crown head are integrally formed. Thus, in the screw lock operation for engaging the crown in the male screw section of the winding stem pipe, since the crown shaft section is also turned, the winding stem connected to this crown shaft section is also turned together with the crown.
Consequently, in the application of the present invention to the portable watch having the function of winding up the spiral spring, the spiral spring is wound up as the crown is engaged with the male screw section of the winding stem pipe. A winding-up operation for the spiral spring is performed by manual winding or automatic winding. However, it is impossible to know in which winding state the spiral spring in the case band is. Therefore, in a state in which the spiral spring is wound up to a considerable degree, the screw lock operation with respect to the crown may be performed. In this case, the screw lock operation becomes particularly heavy, which is inconvenient. Accordingly, an excessive operation force is applied to the male screw section and the female screw section, and abrasion of these screw sections is accelerated.
Further, in the application of the present invention to the portable watch having the function of changing an operation mode, an operation mode is changed freely following the screw lock operation with respect to the crown. Consequently, the technique, which utilizes engagement of screws to prevent a crown from being turned carelessly, cannot be applied to the portable watch of this type.
A problem that the present invention is to solve is in providing a portable watch in which a crown can be held so as not to be turned carelessly utilizing engagement of screws without being restricted by a function of a watch movement, durability can be improved, and a screw lock operation for the crown is light.